automobile assembly painting: energy and environmental impacts
TRANSCRIPT
Automobile Assembly Painting: Energy and Environmental Impacts
Lecture # 36
Prof. John W. Sutherland
Adapted from materials ofProf. David R. Shonnard, Ph.D.
Dept. of Chemical EngineeringMichigan Technological University
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Lecture Outline
!Automobile Manufacturing and Painting
!Energy Model Results" Energy Consumption, Costs,
Environmental Impacts!Energy Minimization Analysis
Results
Body Parts
Powertrain
Components
RawMaterial
RawMaterial
RawMaterial
Stamping/Molding Machining
SurfaceTreatment Welding
Painting Sealers &Adhesives
Casting Machining
Manufacturing Painting
FinalAssembly
Air emissions
Solid waste
Waste water
Oil waste
Oil mist
Scrap
Vehicle Production
Jerry D. Rogers, GM Research and Development Center
Automobile Manufacturing
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Overall Auto Assembly Plant Process Flow
Body Shop
Paint Shop
Final Assembly
T. Lawrence, U. GA
Paint Shop Process FlowPhosphate Electrocoat Paint
E-Coat Oven
From Body Shop
Sealer Primer Paint
Primer/Sealer Oven
Basecoat Paint
ClearcoatPaint
Topcoat Oven
Flashoff
T. Lawrence, U. GA
Paint Spray Booth General Design
T. Lawrence, U. GA
Process Flow Diagram for Automobile Assembly Painting
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Introduction and Background
!Why Analyze Assembly Painting?" Consumes 50% of assembly plant
energy" Approximately 10-20% of all energy
used is for assembly plant painting
!Future Paint Issues" Solvent → Water-based → Powder
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Phosphate Unit
!Purpose is to prepare body surface for painting" Cleaning solution" Rinse stages" Phosphate dip tank" Rinse stages
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Electrocoating Tanks and Ovens!Purpose is to prevent corrosion of
body surfaces" Body is dipped into a tank " DC current is applied within tank" Washing step to remove excess
solution" Drying oven (~215˚C) removes
excess solvents into an air stream that is directed to air pollution abatement equipment
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Sealer Booths and Ovens
!Purpose is to prevent rust" joints between body parts" body surfaces near road surfaces
!Booth where sealant is applied by robots
!Oven where sealant is cured" Air stream in oven is directed to
pollution abatement equipment
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Prime Coat Booths and Ovens! Purpose is to provide a bonding
surface between Electrocoat and the Basecoat" Contains solids, fast volatilizing solvents,
and slow volatilizing solvents" Fast volatilizing solvents removed in
booths" Booths at 70˚F and 70% relative humidity" Slow volatilizing solvents removed in
ovens" Ovens at ~155˚C" Oven air directed to pollution abatement
equipment
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Basecoat/Clearcoat Booths & Ovens
!Apply final color and clear coat overlay" Operation of ovens similar to prime
coat
Paint Spray Booth General Design
Exhaust
Sludge water to capture paint overspray
Filter
Laminar downdraft
Paint spray
T. Lawrence, U. GA
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
The Carbon Wheel
Regenerative Thermal Oxidizer: VOC Abatement
Process Flow Diagram for Automobile Assembly Painting
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Typical Booth Environmental Design Conditions
!Higher airflow for manual paint spray zones versus automatic (robotic) spray zones
!Typical paint booth conditions" Downdraft velocity
• Manual zones = 100 fpm• Automatic zones: 60 to 80 fpm
" Temperature: 75 to 78°°°° F" Relative humidity: 60±10 %
T. Lawrence, U. GA
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Energy Model Assumptions! Steady-state analysis! Assume booth conditions, 70˚F, 70% RH! Oven temperatures are specific to each oven! Sensible heat and latent heat effects! 1,300,000 scfm air flow rate! 10% to ovens, 90% to booths! 30% of booth air to Carbon Wheel system! 6 RTO units, 88 scfm natural gas for each
unit
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Energy Model ResultsEnergy Source Energy (kJ/yr) Percent of Total
Heat Booth Air Nat. Gas 2.96E+11 28.6RTO Nat. Gas 2.40E+11 23.1BC/CC Oven Nat. Gas 1.10E+11 10.6Booth Air Flow Electric 7.62E+10 7.4Prime Oven Nat. Gas 7.45E+10 7.2E-coat Oven Nat. Gas 6.49E+10 6.3Phosphate Nat. Gas 5.92E+10 5.7CW Nat. Gas 5.84E+10 5.6Sealer Oven Nat. Gas 2.30E+10 2.2RTO Electric 1.49E+10 1.4E-coat Booth Electric 1.05E+10 1.0Oven Air Flow Electric 6.53E+09 0.6Phosphate Electric 9.53E+08 0.1CW Electric 8.58E+08 0.1
1.04E+12 100.0
Total 1.04E+12 100
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Environmental Impacts of Energy Use
! Impacts of energy consumption" Natural gas (NG) and electricity (assumed
from coal)" Greenhouse gas emissions, CO2" Criteria pollutants: SOx, NOx, CO, VOC,
PM10" Toxic (EPCRA) and hazardous (RCRA)
pollutants! Impacts of producing NG and coal
" EIO-LCA web site at Carnegie Mellon University
" www.eiolca.net
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Impacts of Energy Consumption
EnergyConsumption(kJ/yr)
÷Fuel Value(kJ/kg fuel)
÷Fuel HeatingEfficiency
xPollutantEmissionFactor(kg/kg fuel)
=PollutantEmissionRate(kg/yr)
ToxicsCO2
SOxNOxCOVOCPM10
RCRA
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Impacts of NG/Coal Production
EnergyConsumption(kJ/yr)
÷Fuel Value(kJ/kg fuel)
xFuel Cost($/kg fuel)
EIO-LCA
=PollutantEmissionRates(kg/yr)
ToxicsCO2
SOxNOxCOVOCPM10
RCRA
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Composite Environmental Index! Normalization: use national emissions data
" For each pollutant! Valuation: weight each category of emission
" EcoIndicator 95 method - European studies
Environmental Index Weight National Inventory (103 kg/yr)Toxics 5 1.3x106
CO2 2.5 5.5x109
SOx 10 1.8x107
NOx 2.5 2.1x107
PM10 2.5 2.8x107
VOC 2.5 1.9x107
RCRA 5 2.6x108
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Environmental/Cost ResultsEnergy Source
Operating Cost per Year
% of Total Cost
% Env. Impact
Temperature In/Out
Heat Booth Air Nat. Gas $1,968,777 21.2 3.9 11.1/21.1Air Flow Booths Electric $1,746,884 18.8 49.1RTO Nat. Gas $1,591,962 17.2 3.1 152/207E-coat Booth Electric $843,219 9.1 23.7
BC/CC Oven Nat. Gas $729,593 7.9 1.4 11.1/177Prime Oven Nat. Gas $494,475 5.3 1.0 11.1/154E-coat Oven Nat. Gas $430,910 4.6 0.9 11.1/210Phosphate Nat. Gas $392,893 4.2 0.8CW Nat. Gas $387,833 4.2 0.8 11.1/127RTO Electric $341,513 3.7 9.6Sealer Oven Nat. Gas $152,727 1.6 0.3 11.1/138Air Flow Ovens Electric $149,733 1.6 4.2Phosphate Electric $21,850 0.2 0.6CW Electric $19,656 0.2 0.6
$9,272,024
Total $9.27E+6 100 100
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Energy Conservation Targeting: Pinch Analysis
! Graphical Pinch Analysis to examine the feasibility of waste energy recovery
! Only the RTO exhaust was used as hot stream
! All incoming air streams are combined into a composite cold stream
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Pinch Analysis Results
0
50
100
150
200
250
4.0E+07 8.0E+07 1.2E+08Heat Load (kJ/hr)
Tem
per
atu
re (
C)
Cold (shifted)Hot Stream
0
Energy transferredby a network of heatexchangers
Energy transferred by external utilities
Booth Air +all streams
All streams -Booth Air
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Heat Integration
!Encouraged by the pinch and energy flow found while modeling
!Two different approaches examined" Recycling of process material
stream(s)" Heat integration using a heat transfer
fluid (HEN: heat exchanger network)
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Heat Integration via Recycle! Maximum energy reduction of only 4%! Environmental impact reduction of
about 3%! Economically feasible, and simple to
accomplishCW clean air to booth robotic zones Carbon Wheel to Ovens Manual zones to Robotic zones% Make up air 30 % Air flow needed 130000 scfmAir flow needed 351000 scfm Air flow available 351000 scfm Air flow needed 351000 scfmAir available 351000 scfm Air flow available 819000 scfmFresh air added 105300 scfm Energy Saved 1.67E+10 kJ/yrAir recycled then 245700 scfm Energy saved 4.51E+10 kJ/yr
Money Saved $110,918 per yearEnergy Saved 3.16E+10 kJ/yr Money saved $299,478 per year
Cost savings 209,635$ per year
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
HEN Economic Evaluation! 10 year period! 7 year MACRS depreciation scheme! Income from reduction in energy cost! Operating cost from pumping of heat
transfer fluid and maintenance! Sizing of exchangers uses constant
value of the heat transfer coefficient! Cost of exchangers uses a .6
exponential function
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Economics & Env. Impact Reduction of HEN RTO to Booth, Recovery of 2.96x1011 kJ/yr
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
Conclusions! Over half of the process energy is lost
through the RTO exhaust! Heat integration using intermediate
fluid appears to be economically feasible and reduces overall environmental impact
IRR
Corperate Energy Recovered
Plant Env. Impact Reduction
Plant CO 2
Impact Reduction
Booths set ambient & recovery 0.4 6.51% 4.2 17.8Booths seasonal Econ: 0.317 5.65% 4.7 13.0 Env.: 0.306 6.34% 5.7 15.8Ovens seasonal Econ: 0.334 5.02% 6.0 13.8 Env.: 0.289 6.95% 7.8 19.0
Environmentally Responsible Design & Manufacturing (MEEM 4685/5685)Dept. of Mechanical Engineering – Engineering MechanicsMichigan Technological University© Shonnard/Sutherland
ReCap! Automobile assembly painting is an important
energy consuming process in the manufacturing life-cycle.
! Environmental impacts are related to the energy consumption, wastewater, paint solids, and volatile organic compounds (VOCs).
! Heating of inlet air for booths and ovens is the major energy consuming element.
! Energy conservation alternatives can be evaluated using Pinch Analysis coupled with Heat Exchanger Network (HEN) synthesis.